The present invention relates to the function of limiting the total or storage-system-wide amount of occupied disk spaces (hereinafter called a total disk usage amount) of a user or a user group in an environment involving a plurality of network storage. The term “user” is hereinafter defined as a single user or a user group including a plurality of users.
In the prior art, the data of a client is stored in a storage directly connected to the client (direct attached storage: DAS), and the data on the DAS is accessible only through the client directly connected. With the recent development of the network technique, however, a method has been spreading in which the storage is separated from the client and connected to the network so as to be accessible through the network. The storage connected to the network in this way is called the network storage (NAS). The NAS makes it possible to share the data among a plurality of clients, and therefore the manager can manage the shared data efficiently.
In the case where the amount of the data shared by a plurality of clients is increased to such an extent as to exceed the disk capacity of a single NAS, the manager adds a new NAS. The addition of a new NAS solves the problem of disk capacity. Nevertheless, each time a NAS is added, the setting in the system is required for all the clients, thereby leading to an increased management cost. As a method of suppressing the management cost, a virtually unifying technique for NAS has been under study in which a plurality of NASs are caused to appear as a single NAS from the clients and the whole system is not affected by the addition of a new NAS.
In the case where a plurality of users share a NAS and a given user sharing the NAS uses a great amount of disks in the NAS, on the other hand, the use of the disks by other users sharing the NAS is inconveniently limited. In order that a user sharing the NAS may not limit the use of other users inconveniently, the user's act to use the disks of the NAS is required to be limited. Means generally used for this limitation is the function to limit the disk usage amount of each user (quota function).
An example of the virtually unifying technique for NAS is described in http://potal2.ligato.com/resources/detasheets/D124.pdf (reference 1). According to this method, a NAS called primary storage manages the file location information in a centralized manner, so that a plurality of NASs are caused to virtually appear as a single NAS.
Another method for virtualizing multiple NASs is described in DiFFS: a Scalable Distributed File System, Christos Karamanolis et. al., HP Laboratories Palo Alto, HPL-2001-19, Jan. 24, 2001 (reference 2). The method is that a plurality of NASs are caused to appear as a single NAS by a non-centralized management server system different from the centralized management server system described above.
According to the function known as the disk usage amount limiting function, the manager sets an upper limit of the disk usage amount of each user for the NAS. The user for whom the upper limit of disk usage amount has been set cannot write into NAS beyond the particular disk usage amount upper limit even in the case where the NAS has a sufficient residual capacity. The NAS having the disk usage amount limiting function, upon receipt of a write request from a user, judges the limit of the disk usage amount. In the case where the set upper limit of disk usage amount is exceeded by the disk usage amount of the user due to the write request, an error (quota error) to the effect that the disk usage amount upper limit has been exceeded is notified to the particular user, who is subsequently prohibited from issuing a write request for using a new disk area.
In the prior art, this disk usage amount limiting function is packaged in the OS or file system of the NAS, and has worked for each NAS. For example, the disk quota in the FreeBSD constituting a free operating system or in NTFS5 of Windows 2000 (trade mark) of Microsoft works for each computer. In the case where a single NAS runs short of capacity and a plurality of NASs are used as described above, however, the function is required to limit the disk usage amount totally or storage-system-widely (hereinafter called “totally”) for a plurality of NASs but not for each NAS.
A technique for limiting the disk usage amount totally for a plurality of NASs as a whole is described in U.S. Pat. No. 5,819,047 (reference 3). The feature of this technique lies in that the upper limit of disk usage amount is stored for each user in a storage-system-wide or unified account data base (hereinafter called a unified account data base) for a plurality of NASs, and each time the user attempts to write in NAS, the account data base is requested to determine whether the NAS is available for use or not.
US Patent Publication No. 2002/0,023,156 (reference 4), on the other hand, discloses a method of improving the efficiency of the disk usage amount limiting function for a system comprising a plurality of computers and one or a plurality of shared storage. The residual disk capacity available for each user is distributed to each computer in the form of reserved space beforehand, and upon receipt of a write request from the user, the limit of disk usage amount for the particular computer is judged, and the value of the reserved space held locally by the computer is manipulated to suppress the inquiries from the computer to the shared storage with respect to the residual disk capacity available for use through a network, thereby improving the efficiency.